This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
When using TCPmon, your needs to send requests to TCPmon which in turn forwards the requests to the real service endpoint.
Thus, if TCPmon is listening on port 8888, you should change the web service to listen on another port (8080 in your example).
If you want to monitor a client-server interaction without changing the client or the service, use a tool like WireShark.